Risk ratios of lung cancer associated with an increase of 10 µg/m3 in PM2.5 in the random 5% sample of Urban Employee Basic Medical Insurance beneficiaries*
| Number of cities | Total beneficiaries | Low polluted area† | High polluted area† |
| No. of city=36 | No. of city=7 | No. of city=29 | |
| 1-year | 1.09 (0.98 to 1.21) | 1.06 (0.94 to 1.21) | 1.22 (0.83 to 1.79) |
| 3-year | 1.12 (1.00 to 1.26) | 1.01 (0.86 to 1.18) | 1.69 (1.09 to 2.64) |
| 5-year | 1.11 (0.98 to 1.26) | 1.00 (0.84 to 1.19) | 1.64 (1.04 to 2.58) |
| 10-year | 1.11 (0.98 to 1.26) | 1.01 (0.85 to 1.20) | 1.59 (1.00 to 2.54) |
*Risk ratios and 95% CIs were calculated on the basis of an increase of 10 µg/m3 in PM2.5. Risk ratios were adjusted for calendar time, region and smoking rate.
†PM2.5 concentration was modelled as linear spline with a cut-point at 35 µg/m3; cities with annual mean PM2.5 concentration under 35 µg/m3 were classified as low exposure group.
PM2.5, particulate matter with an aerodynamic diameter of less than 2.5 μm.